Cu – Free Click Chemistry (SPAAC)(Figure 1). Schematic representation of a SPAAC ligation reaction.The strain promoted alkyne-azide cycloaddition, also termed as the Cu-free click reaction, is a bioorthogonal reaction utilizing a pair of reagents, cyclooctynes and azides that exclusively and efficiently react with each other while remain inert to naturally occurring functional groups such as amines (Figure 1). SPAAC enables labeling a wide varie…